An air compressor system is often pressurized with a motor driven compressor controlled by a pressure-operated switch that senses pressure in an air receiver such as a pressure vessel. The compressor forces compressed air through a discharge tube and a check valve which is connected to a pressure vessel, the pressure vessel serving as a reservoir for storing the compressed air. When the pressure of the compressed air being produced and stored in the pressure vessel reaches a preselected maximum level, the pressure switch shuts off the compressor motor to stop further pressurization. The lack of pressure from the compressor allows the check valve to close, preventing air from flowing from the air receiver back into the discharge tube when pressurization stops. However, pressurized air may still remain in the discharge tube and in the head of the compressor.
As air is consumed from the pressure vessel, the level of pressure remaining within the pressure vessel is reduced. When the pressure in the pressure vessel falls to a preselected minimum level, the pressure switch again operates the compressor to resume pressurization. However, if the remaining pressure in the discharge tube and in the head of the compressor is not removed prior to resuming pressurization, the compressor must overcome the added load from this remaining pressure in addition to the load of initiating pressurization. This can result in adverse system effects on the compressor motor such as motor stalling or electrical circuit overloading in the circuit in which the motor is installed.
To prevent this, an unloader valve is operated by the pressure switch to relieve the pressure from the discharge tube when the pressure within the pressure vessel rises to a preselected maximum pressure level. Typically, the unloader valve is connected to the discharge tube through an additional hose, tubing, or other mechanical communication means.
One problem which exists with this type of unloading configuration is that it will typically fail to unload the discharge tube and compressor head when the pressurization is interrupted by means other than the pressure switch. For example, in the event of a power failure or when a compressor is unplugged during operation so that the predetermined pressure threshold recognized by the pressure switch is not reached, unloading will not occur. This can leave back pressure on the discharge tube when pressure in the pressure vessel is less than the predetermined threshold value.
In operation, many air compressors are configured to effect pressurization with compression cylinders or other pulsating mechanisms. Such mechanisms effectively establish high pressure conditions within the discharge tube and the head of the compressor to pressurize the pressure vessel. However, the pulsating action of such mechanisms can also lead to pressure pulsations which adversely affect the operation of the check valve. For example, if the check valve incorporates a spring-biased piston assembly, pressure pulsations from the compressor motor can cause one or more components of the piston assembly to reciprocate in response to the pressure pulsations, possibly leading to undesired vibration and check valve damage.
The invention is a check valve for installation between a compressor and an air receiver in an air compressor system. The check valve has an elongated body having a hole extending from an inlet end to an outlet end of the check valve.
An air bleed aperture can extend through the body and can be adjacent a groove extending around the circumference of a valve seat assembly mounted within the hole. The valve seat assembly can have a check valve seat facing the outlet end of the body, and a plurality of raised unloader seating elements extending toward the inlet end of the body, and can include a passage from the groove toward the inlet end. An unloader valve seal can be reciprocally mounted to slide within the hole of the check valve between unloader seating elements of the valve seat assembly and the inlet end of the body. A piston assembly mounted within the body can include a piston, a check valve seal, and a piston spring. The piston spring biases the piston to a first piston location that is toward the inlet end of the body which prevents air from flowing from the inlet end toward the outlet end of the valve body. The check valve seal can be positioned on the piston assembly to contact and seal against either the check valve seat of the valve seat assembly or the inside diameter of the hole extending through the check valve body to prevent air flow when the piston is in the first piston location.
The piston assembly can force the unloader valve seal away from the unloader seating elements when the piston is in the first piston location, permitting air to flow from the inlet end of the body to the air bleed aperture. When the air compressor produces sufficient air pressure at the inlet end of the body to force the piston from the first piston location to any of a plurality of downstream piston locations, the unloader valve seal becomes free to slide downstream to contact and seal the unloader seating elements, thereby preventing air from flowing from the inlet end of the body through the air bleed aperture. Movement of the piston from the first piston location to a downstream piston location can also remove the check valve seal from the check valve seat and/or from the inside diameter of the hole extending through the check valve body, allowing air to flow from the inlet end toward the outlet end of the valve body.
The hole extending through the body of the check valve may include a tapered portion having a first inner diameter and at least a second larger inner diameter, the first inner diameter being closer to the inlet end of the check valve than the second inner diameter. A clearance space exists between the check valve seal and the tapered portion of the inner diameter of the hole when the piston moves to a downstream piston location, permitting a level of air flow from the inlet end of the valve body toward the outlet end of the valve body. The clearance space between the valve seal and tapered portion of the inner diameter of the valve body can be greater when the piston is at a first downstream location that is farther away from the inlet end of the valve body than when the piston is at a second downstream location that is closer to the inlet end of the valve body. As a result, the level of air that is permitted to flow from the inlet end of the valve body toward the outlet end of the valve body can be greater when the piston is at the first downstream location than when the piston is at the second downstream location, allowing the check valve to be used with air compressors having different volume output levels.
A dampener may be attached to the outlet end of the valve body. The piston assembly includes a first bumper positioned to remain inside the hole of the valve body. A valve body clearance is maintained between the first bumper and the inside diameter of the hole of the valve body. The piston assembly also includes a second bumper positioned to remain inside the inside diameter of the dampener. Together, the first and second bumpers serve to minimize wear on the piston assembly during operation of the check valve. The piston assembly further includes a dampener seal which may comprise the second bumper or a separate component and which seals the clearance between the piston assembly and the inside diameter of the dampener. A dampener orifice is included with the dampener to restrict the amount of air that can enter the dampener to dampen the movement of the piston.